DESCRIPTION (adapted from application abstract): The smooth pursuit eye movement system is an exemplar of smooth motor control that relies on visual motion processing. Two relatively simple, yet powerful, models have been developed and both adequately describe many characteristics of the smooth pursuit response. The internal structures of the models are very different, and lead to different predictions for a wide variety of stimuli. Adapting procedures and stimuli from the domain of visual psychophysics, we propose experiments that test different components within the smooth pursuit models. Our experiments will also provide data on how the smooth pursuit system responds to stimuli with complex spatial and temporal characteristics. Our approach may also allow us to determine the extent that sensory motion processing limits the initial response of the smooth pursuit system and assess if common stages of motion processing underlying oculomotor and psychophysical performance. We propose to answer the following questions: 1) How precise is the pursuit system, and what limits its precision? 2) How does the pursuit system respond to directional signals? 3) What is the response of the pursuit system to acceleration? 4) What are the effects of backgrounds on smooth pursuit initiation? The results of the proposed experiments should guide further refinements of the current models of smooth pursuit. Experimental results on normal subjects may also provide fresh insights into subtleties of smooth pursuit and aid in the diagnosis of brain dysfunction that affects oculomotor control. The results may benefit strabismics, amblyopes and other individuals suffering from oculomotor pathology.